It is known that a high efficiency solar cell can benefit from point contacts, as this increases the current density in the junctions. Examples include the PERL cell from the University of New South Wales, which achieved 24.7% efficiency, and the back contact cell made by SunPower Corporation of San Jose, Calif. However, such structures are difficult to fabricate at low cost as they require several lithographic steps that are registered to one another.
FIG. 1 shows one conventional junction contact structure. As shown in FIG. 1, a passivating oxide layer 104 is formed on a bulk material 100 to minimize recombination on the surface. Holes are cut in the oxide using photolithography and wet etching, and n(p)-type regions 102 are diffused into the p(n)-type substrate 100. A second registered lithography is then performed to define contacts 106 over the contact holes. Therefore, at least two patterning steps are required, with the second registered to the first. Such patterning is difficult to perform at the high throughput required for a solar cell line (on the order of 3000 wafers per hour for 100 megawatts).
Accordingly, there remains a need in the art for a less complex structure and technique for forming point contacts in a solar cell.